Plasma catalytic fuel injector for enhanced combustion

ABSTRACT

Apparatus and method for enhancing combustion comprises an enclosure defining an opening for introduction of a gas and openings for the introduction of air, with a nozzle in the opening for introduction of a fuel gas into the enclosure. First and second electrodes are located in the enclosure, the first and second electrodes being coated with dielectric material, and being connected to an electrical power supply. With electrical power applied to the first and second electrodes and with the fuel gas sprayed into the enclosure, an atmospheric pressure plasma created by a dielectric barrier discharge is produced in the enclosure that cracks the fuel gas prior to its mixing with air introduced through the openings for the introduction of air.

The present invention generally relates to combustion processes, and,more specifically, to processes that enhance the efficiency ofcombustion processes. This invention was made with Government supportunder Contract No. W-7405-ENG-36 awarded by the U.S. Department ofEnergy. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Combustion processes are involved in many aspects of modern life, andare, in large part, responsible for our current standard of living.Combustion provides the propulsion of our automobiles and airplanes,generates virtually all our electrical power, heats most of our homesand buildings, and provides much of our hot water. In this age ofincreasing energy costs, it is vitally important to assure that thesecombustion processes are carried out in the most efficient way possible,and to assure that fuel is conserved and that pollution is reduced.

All combustion processes involve the breakdown of the fuel being burnedinto free radicals and other reactive species. It is this breakdown intoreactive species that initiates a combustion process. In manyapplications, a spark plug produces a momentary high voltage sparkdischarge that breaks down an air/fuel mixture into the requisite freeradical/ion reactive species so that combination with oxygen and/or fuelcan occur. Combustion then continues by the propagation of the reactivespecies generated by the heat of the reaction itself.

Thus, the overall combustion reaction rate usually is determined by theefficiency of generation of the new reactive species in the spreadingflame front. As the reaction rate and temperature of the combustionprocess are increased, a related increase in detonations and pressurewill occur.

Since the efficiency of combustion processes largely is determined byusual thermodynamic considerations, namely, the higher the temperature,the more thorough and efficient the combustion process becomes,.and thegreater the energy that can be extracted -and the higher the Carnotefficiency. This is the reason behind the thrust of engine makers,either of internal combustion engines or jet engines, to seekever-higher temperature combustion processes. However, this increase intemperature places increasing demands on material scientists to providematerials that can withstand such high temperatures.

The objects, advantages and novel features of the invention will be setforth in part in the description which follows, and in part will becomeapparent to those skilled in the art upon examination of the followingor may be learned by practice of the invention. The objects andadvantages of the invention may be realized and attained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

In accordance with the objects and purposes of the present invention, asembodied and broadly described herein, apparatus for enhancingcombustion comprises an enclosure defining an opening for introductionof a gas and openings for the introduction of air, with a nozzle in theopening for introduction of a fuel gas into the enclosure. First andsecond electrodes are located in the enclosure, the first and secondelectrodes being coated with dielectric material and being connected toan electrical power supply. Wherein, with electrical power applied tothe first and second electrodes and with fuel gas sprayed into theenclosure, an atmospheric pressure plasma created by a dielectricbarrier discharge is produced in the enclosure that cracks the fuel gasprior to its mixing with air introduced through the openings for theintroduction of air. In another aspect of the present invention, and inaccordance with its purposes and objects, a method of increasing theefficiency of combustion processes comprises the steps of producing anatmospheric pressure plasma created by dielectric barrier discharge; andspraying a fuel gas into the atmospheric pressure plasma; wherein theatmospheric pressure plasma cracks the fuel gas.

In still another aspect of the present invention and in accordance withits purposes and objectives, apparatus for enhancing combustioncomprises separate supplies of fuel and air, with valve means forcontrolling the flow of fuel and air. Plasma processing means receivethe fuel and air for selectively pre-cracking the fuel and exciting theair and outputting the pre-cracked fuel and excited air to a combustor.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and forms a part ofthe specification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is an illustration of an embodiment of the present invention inwhich an atmospheric pressure plasma is used to crack the fuel.

FIG. 2 is an illustration of an embodiment of the present invention inwhich a combination of a plasma and heated electrodes are used to crackthe fuel.

FIG. 3 is an illustration of an embodiment of the present invention inwhich valves and individual plasma units are used to show some of thevarious ways that a plasma treatment could be applied to the combustionprocess.

DETAILED DESCRIPTION

The present invention converts liquid or gaseous fuels into reactivespecies on a continuous basis, so that the combustion process does notrely solely on the self-generation of reactive species. Theunderstanding of the invention can be aided through reference to thedrawings.

In FIG. 1, a schematical illustration of one embodiment of the inventionis shown where fuel gas 11 is introduced into volume 12 through fuelnozzle 11 a. If fuel gas 11 is initially in liquid form, such as allhydrocarbon fuels, oxygenated hydrocarbon fuels and other functionalizedfuels, fuel oils, diesel fuels, kerosene fuels including usual jet fuelssuch as Jet A, Jet B, JP-10, crude oil, and kerosene, it is atomized inthe manner of conventional fuel injectors before being introduced intovolume 12. If the fuel gas 11 is a gas, such as propane, natural gas,butane, propene, pure methane, ethylene, ethane and related fuels, it ispassed directly through nozzle 11 a to meter the flow. The presentinvention can use essentially any liquid or gas that burns as fuel gas11.

Because the present invention can accommodate both liquid and gaseousfuels it useful in virtually all present combustion processes. In somecircumstances, it will be beneficial to heat fuel gas 11 before it ispassed through nozzle 11 a to achieve an even higher level ofenhancement.

Electrical power unit 13 produces a voltage at electrodes 13 a and 13 binside volume 12. Each of electrodes 13 a 13 b is coated with dielectricmaterial 13 c. The voltage at electrodes 13 a, 13 b produces anatmospheric pressure plasma created by dielectric barrier discharge involume 12 that cracks fuel gas 11 into reactive species 14. Reactivespecies 14, now a highly reactive cracked fuel, is exhausted throughvolume 12 until it is mixed with air 15 incoming through ports 12 a andcombusts into flame front 16. Further ignition may not be needed asreactive species 14 are predisposed to immediate reaction with oxygen.Hence, this embodiment of the invention can serve as an ignitioninitiator device. To further enhance the cracking process, electrodes 13a, 13 b could be coated with a dielectric material that has a catalyticmaterial deposited at predetermined non-contiguous areas.

Electrical power unit 13 can supply a range of voltages to electrodes 13a, 13 b. In a one embodiment, electrical power supply 13 provides aradio frequency voltage having a frequency of 13.56 MHz. Other possibleoutputs of electrical power supply 13 include pulsed direct current,alternating currents from low frequencies to radio frequency and evenmicrowave. Each will be capable of creating the atmospheric pressureplasma created by a dielectric barrier discharge.

Fuel gas 11, whether atomized or gaseous, is cracked by passing throughthe atmospheric pressure plasma region in volume 12 in a process thatcan be adjusted to produce any desired level of molecular breakdown. Forexample, in the case of propane, the cracking could be limited to justcleaving hydrogen as shown in the following reaction:CH₃—CH₂—CH₃→CH₃—CH₂—CH₂.+H..   10Should it be desired to cleave methylene fragments or carbenestructures, the following reactions would occur:CH₃—CH₂—CH₃→CH₃—CH2.+CH₃.   11CH₃—CH₂—CH₃→2CH₃.+CH₂:   12

Another embodiment of the invention is illustrated schematically in FIG.2. In this embodiment, which is similar to that shown in FIG. 1,electrical power unit 13 is connected to electrodes 21 a, 21 b, whichmay be fabricated from any metallic materials, and which are coated witha dielectric material having, in one embodiment, known transitionelements, such as platinum, or alloys made of combinations of transitionelements, deposited at predetermined non-contiguous areas. To achievesimilar results, a catalyst such as platinum or other transitionelement, could be suspended inside volume 12.Electrodes 21 a, 21 b alsocan be resistance heated by power sources 22, 23 to add thermaldeposition to the cracking reactions to further accelerate the cleavagereactions.

Experiments using a configuration as shown in FIG. 1 have shown thebenefits of plasma-enhanced combustion. Propane was combusted in acoaxial tube with an atmospheric pressure plasma present showedsignificant differences when compared to combustion with the plasma notpresent. Among these differences are (1) an enhanced flame front 16(FIG. 1) that was more stable and less prone to “blow out;” (2) thephysical character of flame front 16 was visually different; (3) and,most importantly, residual unburned propane was measurably reduced asshown by mass spectrometry. The amount of efficiency enhancement isstill under investigation and optimization of the propane combustionprocess is progressing. In unoptimized experiments with activatedpropane mixed with air, an increase in propane utilization ofapproximately 88% was observed, with a concomitant increase of carbondioxide and water production (indicators of better combustion) ofapproximately 130% and 67%, respectively, was observed.

Another embodiment of the invention that may provide improved pollutantemission performance and excellent control is illustrated in schematicform in FIG. 3. Here, fuel supply 31 provides fuel as previouslydescribed to valves 32, 33, and 34. Air supply 36 provides air to valves37, 38, and 39. With valves 32 and 37 open, fuel and air can mix inT-connection 35 and be provided to combustor 40 if valve 41 is open.This would be for conventional combustion. Alternatively, if only valves34 and 39 are open, fuel and air would separately be provided tocombustor 40.

However, to achieve the benefits of the present invention, valves 34,39, and 41 would be closed and valves 32, 37, and 42 opened. In thisarrangement, the mixed fuel and air flows through plasma unit 42 wherefuel is cracked and air is excited, in a process previously described,before entering combustor 40. However, there is no present evidenceindicating that subjecting the fuel-air mixture is superior to using theplasma to crack only the fuel prior to its mixing with air. If desired,the fuel and air could separately pass through plasma units 44 and 45respectively if valves 33 and 38 are open and all other valves closed.According to the desired effect, any or all of the valves may be partlyopen with some of the fuel, the air, or a mixture of both undergoestreatment by the plasma.

From FIG. 3, it is easy to understand how this embodiment of the presentinvention can provide the most efficient operation of combustor 40.Configurations ranging from no plasma pre-cracking to complete plasmapre-cracking of any stream of air and/or fuel can be easily obtainedthrough control of the valves.

The foregoing description of the embodiments of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously many modifications and variations are possiblein light of the above teaching. The embodiments were chosen anddescribed in order to best explain the principles of the invention andits practical application to thereby enable others skilled in the art tobest utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto.

1. Apparatus for enhancing combustion comprising: an enclosure definingan opening for introduction of a gas and openings for the introductionof air; a nozzle in said opening for introduction of a fuel gas intosaid enclosure; first and second electrodes located in said enclosure,said first and second electrodes being coated with dielectric material,and being connected to an electrical power supply; wherein, withelectrical power applied to said first and second electrodes and withsaid fuel gas sprayed into said enclosure, an atmospheric pressureplasma created by a dielectric barrier discharge is produced in saidenclosure that cracks said fuel gas prior to its mixing with airintroduced through said openings for the introduction of air.
 2. Theapparatus as described in claim 1 wherein said fuel gas is an atomizedliquid fuel.
 3. The apparatus as described in claim 1 wherein said fuelgas is propane.
 4. The apparatus as described in claim 1 wherein saidfuel gas is natural gas.
 5. The apparatus as described in claim 1wherein said fuel gas is atomized Jet A fuel.
 6. The apparatus asdescribed in claim 1 wherein said fuel gas is atomized Jet B fuel. 7.The apparatus as described in claim 1 wherein said fuel gas is atomizedJP-10 fuel.
 8. The apparatus as described in claim 1 wherein saiddielectric material has a catalytic material deposited onto it atpredetermined non-contiguous areas to enhance cracking of said fuel gas.9. The apparatus as described in claim 8 wherein said catalytic materialis at least one transition element.
 10. The apparatus as described inclaim 8 wherein said catalytic material is an alloy of two or moretransition elements.
 11. The apparatus as described in claim 8 whereinsaid at least one transition element is platinum.
 12. The apparatus asdescribed in claim 1, wherein said electrical power supply providesradio frequency power having a frequency of 13.56 MHz.
 13. The apparatusas described in claim 1, wherein said electrical power supply providespulsed direct current power.
 14. The apparatus as described in claim 1wherein said electrical power supply provides sub-radio frequencyalternating current power.
 15. A method of increasing the efficiency ofcombustion processes comprising the steps of: producing an atmosphericpressure plasma created by dielectric barrier discharge; spraying a fuelgas into said atmospheric pressure plasma; wherein said atmosphericpressure plasma cracks said fuel gas.
 16. The method as described inclaim 15, wherein said fuel gas is an atomized liquid fuel.
 17. Themethod as described in claim 15, wherein said fuel gas is propane. 18.The method as described in claim 15, wherein said fuel gas is naturalgas.
 19. The method as described in claim 15, wherein said fuel gas ispure methane.
 20. The method as described in claim 15, wherein said fuelgas is atomized Jet A fuel.
 21. The method as described in claim 15,wherein said fuel gas is atomized Jet B fuel.
 22. The method asdescribed in claim 15, wherein said fuel gas is atomized JP-10 fuel. 23.The method as described in claim 15, further comprising the step ofheating said fuel gas before said fuel gas is sprayed into saidatmospheric pressure plasma.
 24. The method as described in claim 15,wherein said atmospheric pressure plasma is produced using an electricalpower supply.
 25. The method as described in claim 24, wherein saidelectrical power supply provides radio frequency power.
 26. The methodas described in claim 24, wherein said radio frequency power has afrequency of 13.56 MHz.
 27. The method as described in claim 24, whereinsaid electrical power supply provides pulsed direct current power. 28.The method as described in claim 24, wherein said electrical powersupply provides sub-radio frequency alternating current power. 29.Apparatus for enhancing combustion comprising: separate supplies of fueland air; valve means for controlling the flow of fuel and air; plasmaprocessing means receiving said fuel and air for selectivelypre-cracking said fuel and exciting said air and outputting saidpre-cracked fuel and excited air to a combustor.
 30. The apparatus asdescribed in claim 29, wherein said fuel is pre-cracked prior to beingoutput to said combustor, and said air is output directly to saidcombustor.
 31. The apparatus as described in claim 29, wherein said airis excited prior to being output to said combustor, and said fuel isoutput directly to said combustor.
 32. The apparatus as described inclaim 29, wherein said fuel is pre-cracked and said air is excited priorto being output to said combustor.